So-called avionic systems comprise all the electronic, electrical and computer equipment that assist the control of aircraft.
Historically, avionic equipment has consisted of separate modules communicating with one another by means of unidirectional links and potentially synchronous communication protocols. In this architecture, each of the various avionic equipments (for example, a flight management system, a flight guidance system, a terrain alert system or a display) communicates separately with the equipment with which it must interact in accordance with a potentially synchronous point-to-point or point-to-multipoint communication. In the context of unidirectional communication means, a unit is either a transmitter or a receiver of data. When the transmission of the data between two units must be effected in both directions, first transmission means transmit the data from the first unit to the second and second transmission means transmit in the opposite direction.
Point-to-point communication between two remote units may notably be effected via an ARINC 429 bus (from the name of the company Aeronautical Radio, INCorporated, which publishes the standards defined by the AEEC (Airlines Electronic Engineering Committee) relating to aircraft internal buses and networks and protocols used in aeronautics). The ARINC 429 bus, which may also be referred to as the A429 bus in this application, is standardized. It comprises a physical layer composed of an armored twisted pair and a transport layer. The transport layer may be used in accordance with various protocols for communication between avionic equipments. The protocols used by these units to communicate may be synchronous. For example, in the context of the Williamsburg file transfer protocol, defined by the ARINC 429 P3-18 standard, an avionic equipment must request authorization to send data, by sending a “Request to send” message to a receiver unit, which must authorize the sending of data by sending a “Clear to send” message. An ARINC 429 bus is a unidirectional communication bus comprising a single transmitter and up to 20 receivers.
In some cases, point-to-point communication between two avionic equipments may be performed using a shared memory. This is the case in some avionic system architectures, for example, for communication between the flight management system and the flight control system, in order to allow faster transmission of information. The transmission of information is then also effected in a synchronous manner: in order to prevent concurrent access to the shared memory, a memory area indicates if the memory is being written and can be read or not. Communication between the flight management computer and the flight control computer is performed bidirectionally, the two units exchanging information inside the shared memory. In particular, the flight management computer can send guidance orders to the flight guidance computer. Conversely, the flight guidance computer can send information to the flight management computer advising it of its status and what guidance orders are expected.
Avionic system architectures based on unidirectional links have some limitations. In particular, the number of links increases very rapidly with the number of avionic equipments. This makes adding new units to the avionic system more complicated. Moreover, in the case of ARINC 429 bus links, the installation of a large number of cables increases the weight of the aircraft.
In order to alleviate these drawbacks, modular avionic system architectures have been designed. For example, the AFDX bus (Avionics Full-DupleX Ethernet switching), standardized by the ARINC 664 standard, part 7, proposes an Ethernet type bus complying with specific safety constraints. Whilst preserving the flexibility and the global functioning of an Ethernet bus, it incorporates redundancy for sending packets and a packet switching system managing queues so that only one packet at a time circulates on the network. This system makes it possible to avoid data packet collisions and to ensure deterministic transmission of data that is indispensable for an aeronautical system.
An avionic system with an architecture based on an AFDX bus is much more adaptable than a system based on unidirectional links. In fact, it suffices in order to add a unit to connect it to the AFDX bus and to assign it a network address, rather than creating and testing separately new unidirectional connections. Moreover, once the equipment has been installed, it is possible to add to it additional functionality simply by updating the software. Communication over an AFDX bus is not synchronous: each unit sends data packets to a target unit, and packets can be sent simultaneously in the network, their circulation being controlled in such a manner as to prevent collisions. Moreover, communications on an AFDX bus are simultaneous multi-directional: two units can transmit data to each other simultaneously via the same AFDX data bus.
AFDX bus installation has facilitated the adoption of new equipment in aircraft. Also, numerous recent functionalities have been developed for flight management computers communicating via an AFDX network. Amongst these recent functionalities, CDA (Continuous Descent Approach) procedures make it possible to save fuel as aircraft descend. These functionalities would be complex to redevelop for a flight management computer using synchronized links. Similarly, it is relatively easy to deploy new elements, for example tactile interfaces offering improved performance in an avionic system in which communication between units is based on an AFDX bus.
It is much more complicated to add new functionalities to an aircraft as and when they are designed when communication between elements was initially designed to use a point-to-point synchronous mode. This problem is particularly important where the flight management system is concerned, to which new functionalities are regularly added, notably enabling fuel saving.
A naïve solution to this problem consists in replacing all the avionic equipment of an aircraft with equipment communicating using an AFDX bus. This solution is in practice inoperable. It is in fact extremely costly and forces immobilization of the aircraft for a time period that is unacceptable for an airline.
The patent US20070127521 describes a method for converting messages in accordance with heterogeneous buses or protocols, for example an AFDX bus and an ARINC 429 bus. However, it proposes only direct conversion of packets between two buses and therefore does not address the problem of synchronization of the communication channels. An avionic equipment where communication is based on the AFDX bus would therefore have to emulate synchronous communication as defined in a protocol conforming to the ARINC 429 standard, for example by sending messages conforming to the Williamsburg protocol on an AFDX bus. Moreover, it does not address other types of communication between avionic equipments, such as communication using shared memory.
In order to solve the aforementioned problem, one object of the present invention is to propose an avionic system enabling the insertion of a flight management computer with communication based on a multidirectional channel, for example an AFDX bus, into a set of avionic equipments utilizing synchronous communication.